Browsing by Author "Chang, BJ"

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An off-focus optical tweezers : A new tool for capturing and manipulating a group of particles
(2003)
Chang, BJ
;
Hsu, L
;
Chi, S
;
光電工程學系
;
Department of Photonics
A typical optical tweezers(1) system is operated by precisely focusing a laser beam through an objective into a laser point on the sample plane of a microscope. This results in the trap of a single particle into the laser point via gradient dipole force(2). In the past decade, such in-focus optical tweezers have been widely used in capturing, moving, and manipulating a single bio-cell or a single bead(3). However, it will be useful sometimes to capture a group of bio-cells at a time. For this purpose, we propose a novel technique in this paper by shifting the focusing laser point slightly above or below the sample plane, which leaves a relatively large laser spot on the sample plane. We term this type of setup an off-focus optical tweezers. In this paper, we will demo the capture of a group of polystyrene beads by our off-focus optical tweezers system. In addition, by using a water-drag-force method, we show that the off-focus optical tweezers exhibit a larger transverse capturing range but a weaker trapping force within than the traditional in-focus optical tweezers do.
Automation of an optical tweezers
(2000)
Hsieh, TM
;
Chang, BJ
;
Hsu, L
;
光電工程學系
;
Department of Photonics
Optical tweezers is a newly developed instrument, which makes possible the manipulation of micro-optical particles under a microscope(1). In this paper, we present the automation of an optical tweezers which consists of a modified optical tweezers, equipped with two motorized actuators to deflect a 1W argon laser beam, and a computer control system including a joystick. The trapping of a single bead and a group of lactoacidofilus was shown, separately. With the aid of the joystick and two auxiliary cursors superimposed on the real-time image of a trapped bead, we demonstrated the simple and convenient operation of the automated optical tweezers. assign a new location for the trapped bead to move to. By steering the joystick and then pressing a button on it, we The increment of the motion, 0.04 mu m for a 20X objective, is negligible. With a fast computer for image processing, the manipulation of the trapped bead is smooth and accurate. The automation of the optical tweezers is also programmable. This technique may be applied to accelerate the DNA hybridization in a gene chip(2). The combination of the modified optical tweezers with the computer control system provides a tool for precise manipulation of micro particles in many scientific fields.
Influence of the condenser on sample tracking via forward scattering pattern detection
(2004)
Tsai, CL
;
Chang, BJ
;
Huang, KL
;
Hsu, L
;
電子物理學系
Sample tracking with a high spatial sensitivity is highly desired in force measurement with optical tweezers. However, the trick that sample tracking via forward scattering pattern detection would provide a higher sensitivity than that via regular image detection has never been investigated. In this paper, we systematically study the influences of the position and the numerical aperture of the condenser on sample tracking via forward scattering pattern detection. In our experiment, a 60X condenser is used to form the forward scattering pattern of a sample bead upon a CCD camera. As the bead is transversely shifted at a step size of 30nm by a PZT XYZ stage, we measure the magnitude of the corresponding shift of the forward scattering pattern when the 60X condenser of different angular apertures is placed at various locations along the optical axis. Our result shows that the most sensitive forward scattering pattern occurs when the condenser collimates the forward scattering light from the sample bead. We also find that the larger the numerical aperture is, the higher the sensitivity of forward scattering pattern detection will be.
Observing the dynamic variation of the binding force between rhodostomin ligand and integrin alpha(IIb)beta(3) receptor using a photonic force microscope
(2004)
Chang, BJ
;
Hsieh, CF
;
Lin, CH
;
Chi, S
;
Hsu, L
The conformational change of integrin alpha(IIb)beta(3) plays an important role in clot formation. However, the correlation between the structure and the function of integrin beta(IIb)beta(3) in interacting with its ligand is still not clear. In this report, we focus on the dynamic variation of the binding between integrin alpha(IIb)beta(3) and its ligand, rhodostomin by using a photonic force microscopy (PFM). The PFM is used to trap a rhodostomin-coated bead and, then, shift it to bind a surrounding CHO alpha(IIb)beta(3) cell. Meanwhile, it tracks, with a resolution of 1MHz, the Brownian fluctuations of the trapped bead. Theoretically, the smaller the amplitude of the Brownian fluctuations, the stronger the stiffness of the binding force between the rhodostomin and the CHO alpha(IIb)beta(3) cell. Experimentally, a significant decrease of the Brownian fluctuations was observed during the interval between the 360(th) seconds and the 400(th) seconds after the trapped rhodostomin-coated bead contacted an integrin-expressed CHO alpha(IIb)beta(3) cell. This observation reveals that it takes the rhodostomin 360 seconds to seek the correct position to bind to the integrin alpha(IIb)beta(3). After 400 seconds, the rhodostomin has bound rigidly with the integrin alpha(IIb)beta(3) We presume that the integrin alpha(IIb)beta(3) has reached its final stage of conformational change.
Rapid and simple automatic trapping-force calibration system for optical tweezers
(2005-11-01)
Chang, BJ
;
Hsu, L
;
Chi, S
;
電子物理學系
;
光電工程學系
The automation of a rapid and simple trapping-force calibration system is desired for optical tweezers to measure biological forces. One simple calibration method, the water-dragging-force method, is to calibrate the trapping force against a given water dragging force with an image-processing technique. However, the conventional image-processing technique is too slow because of the time it takes for image recording, transferring, storing, and retrieving. The pattern recognition technique of our automated calibration method is rapid and simple, because it directly processes the image signal without recording, storing, and retrieving any image. In an experiment, we have combined the dragging force method with the real-time pattern recognition technique to calibrate the relationship between the trapping force at a given laser power and a displacement of a bead. We demonstrate the calibration results of the trapping forces on two target beads 10 and 6.2 mu m in diameter, separately, at two laser powers, 5 and 10 mW. Each calibration procedure is finished in 5 min at a pattern recognition rate of 10 Hz with a spatial resolution of 75 nm. We believe that this technique is reliable and rapid enough to be applied to biological force measurement. (c) 2005 Society of Photo-Optical Instrumentation Engineers.